Over the recent past, industry has recognized the importance of monitoring the fuel consumption of internal combustion engines. Such engines exhibit different rates of fuel consumption under various loading and associated operating conditions. With data accurately providing values of substantially instantaneous fuel consumption, engine performance can be evaluated, for example, the evaluation can indicate the physical state of spark plugs, fuel injectors, valves, combustion chamber deposits, and the like.
Business entities engaged in the operation of fleets of trucks and the like are concerned with evaluating the efficiency of the engines within each of their vehicles such that improved scheduling of maintenance can be realized which, in turn, promises savings of larger expenditures otherwise made for excess fuel consumption.
Engine and engine equipment designers recognize the benefits accruing from data representing accurate fuel measurement, for example where various forms of engines are employed with test stands to carry out the design of spark plugs, fuel injectors, and the like. Accurate fuel consumption measurement also is of considerable value in the marine industry. Those charged with the operation of ships and various sea vehicles are continually concerned with the instantaneous values of fuel consumption. This is particularly true where long, open water trips are undertaken. Very often, such trips are planned with only marginal fuel reserves and, thus, an unexpected elevation of fuel consumption or mismanagement of fuel consumption while at sea may endanger both life and property. Accurate fuel consumption monitoring also can be employed both in land and sea vehicle operations to monitor potential fuel leaks which otherwise would be unnoticed.
Typically, fuel consumption monitoring is desired in conjunction with internal combustion engines which employ fuel supply systems which carry out a fuel recirculation function. Such recirculation of fuel commonly is encountered with fuel injected systems and in certain carburetion systems. With these systems, fuel is supplied to the engine in excess of that required for combustion. The excess fuel occurring with this supply is used for the purpose of cooling engine mounted components such as fuel injectors. Following such cooling function, the now heated, return fuel is recirculated to the fuel storage source such as a tank through a common return line.
The commonly accepted approach for measuring fuel consumption for such recirculating fuel supply systems is to employ two flow meters. One of these flow meters is coupled within the supply line to the engine, while the other is positioned within the return line. Fuel consumption then is derived by subtracting the indicated flow rate in the return line from the flow rate in the supply line. This technique for measurement has been found to be quite erroneous, particularly where the engines are being operated at relatively slower rpms, for example at idle and low speed values. In this regard, a typical flow meter will exhibit a relatively high error characteristic for the noted lower and idle speeds. For instance, a conventional instrument rated at 1% of full scale may exhibit errors in the range of about 140% for lower speeds or rates of fuel flow. Correspondingly, at higher rpm and rates of fuel flow, the accuracies of these devices improve to values of about 5%. In consequence, the overall accuracy of such systems generally are found to be unsuitable to the effective early evaluation of engine performance.